It would be advantageous to have a vertebral support device that supports the vertebrae on which it is implanted, while still offering a certain freedom of movement of the vertebrae and, as a consequence, preventing the fusion of these vertebrae, unlike various known osteosynthesis devices.
Various types of osteosynthesis devices are discussed, for example, in patent applications WO02/080788 and WO95/10240 and in U.S. Pat. No. 5,603,714, and U.S. Pat. No. 5,437,669. These devices include at least two bone-anchoring implants, each designed to be anchored to a vertebra and connected together by a linking element (an osteosynthesis bar), using fasteners such as clamps to securely attach the bone-anchoring implants and the linking element. By immobilizing the vertebrae on which it is implanted, this type of device is used to achieve intervertebral fusion, to reduce spondylolisthesis or to correct scolioses or other defects of the spinal column. Also, patent applications WO03/049629, EP 0572790, WO 2005/020829, and WO 00/15125, and U.S. Pat. No. 5,501,684 discuss various types of vertebral anchoring implants facilitating, to varying degrees, the fitting of elements of the osteosynthesis device, the reduction of spondylolisthesis, or the correction of defects of the spinal column. However, these devices provide no freedom of movement of the vertebrae and lead to a fusion of the vertebrae on which they are implanted, which has the disadvantage for the patient of limiting movement and of transferring the stresses normally experienced by these vertebrae onto the adjacent vertebrae and onto the adjacent intervertebral discs. Patent applications WO02/080788, WO03/049629, and WO 2005/020829 are assigned to the assignee of the present application, and are incorporated by reference herein for all purposes.
Other references discuss vertebral support devices comprising osseous anchorage implants linked together by a flexible linking element. For example, U.S. Pat. No. 5,672,175, U.S. Pat. No. 4,743,260, and U.S. Pat. No. 7,083,622 discuss vertebral support devices having implants that are linked together by a flexible bar. These devices allow only a lateral movement, thereby accommodating stresses occurring laterally with respect to the axis of the spinal column but not in the direction of flexion or extension of the spinal column. Patent applications WO 91/16018 (corresponding to patent EP 0 381 588 B1), WO 2004/089244 (corresponding to U.S. Pat. No. 6,966,910 B2) and WO 03/037216 (corresponding to U.S. Pat. No. 6,783,527 B2) discuss vertebral support devices in which the linking element between the implants generally comprise an elastic ligament maintaining a permanent tension between the implants. This type of elastic ligament, used alone, tends to bring the implants together along with the vertebrae on which they are attached, and does not provide an adjustable orientation of the linking element with respect to the implants or of the position of the articulation. Patent applications WO 98/22033 (corresponding to U.S. Pat. No. 6,267,764 B1) and WO 2005/030031 discuss support devices that comprise an elastic ligament fixed to bars linked to the implants, which allows a measure of positioning of the articulation between the implants, but these devices do not necessarily allow an adjustment of the orientation of the bars, and these devices do not provide a central portion absorbing the stresses in compression occurring between the implants. Patent EP 0 669 109 B1, for example, discusses a support device comprising an elastic ligament surrounded by an elastic central portion absorbing the stresses in compression between the implants, and patent application WO 2005/092218 discusses a device comprising an elastic ligament inserted in rigid spacers fitting together and forming a string with the ligament. In these devices, however, the implants rest directly on the central portion or the rigid spacers, which does not permit adjustment of the orientation or the position of the articulation between the implants. U.S. Pat. No. 5,540,688 (corresponding to patent EP 0 516 567 B1) discusses a device comprising an elastic ligament surrounded by a central dampening portion and, in some embodiments, by additional surrounding elements. The position of the ligament with respect to the implants cannot be adjusted, nor can the point of articulation.